Organopolysiloxane resins containing vinyl groups are described in U.S. Pat. No. 3,546,156 to Baronnier et al. These resins are prepared by hydrolyzing phenyltrichlorosilane, trimethylchlorosilane, diphenyldichlorosilane, methylvinyldichlorosilane and dimethyldichlorosilane in the presence of water and thereafter condensing the resultant product in the presence of a diluent and a catalyst while removing the water as it forms. In the process described in this reference, mixtures of silanes having varying ratios of organic to hydrolyzable groups are hydrolyzed and condensed at temperatures above 110.degree. C. to remove the water of condensation in order to form storage stable organopolysiloxane resins, that are substantially free of Si-bonded hydroxyl groups. Compared to the process described in the above patent, the process of this invention has the advantage that the organopolysiloxane resins do not contain at least 25 mol percent of diphenylsiloxane units in order to be flowable. Moreover, the process of this invention, does not require that a mixture of silanes having varying ratios of organic to hydrolyzable groups be used in order to prepare the organopolysiloxane resins of this invention. Furthermore, the organopolysiloxane resins prepared in accordance with the process of this invention are substantially free of Si-bonded hydroxyl groups and may be molded without forming voids. Thus, it is apparent that the process of this invention provides a more direct and improved method for preparing organopolysiloxane resins containing vinyl groups.
Therefore it is an object of this invention to provide a process for preparing organopolysiloxane resins. Another object of this invention is to provide a process for preparing organopolysiloxane resins containing vinyl groups. Still another object of this invention is to provide a method for preparing vinyl containing organopolysiloxane resins which are substantially free of Si-bonded hydroxyl groups. A further object of this invention is to provide a process for preparing vinyl containing organopolysiloxane resins from a mixture containing an organopolysiloxane having Si-bonded hydroxyl groups and an organosiloxane in which at least one of the siloxanes has an average of at least one Si-bonded vinyl group.